1. Field of the Invention
This invention relates to a clamp mechanism for disks used, adapted to clamp a disk as a storage medium, for example, a magnetic disk or an optical disk.
2. Description of the Prior Art
The Applicant has already filed an application for a clamp mechanism for disks, which is capable of clamping a disk used as a storage medium, with a uniform level of force at every part of the disk and maintaining the disk-clamping condition safely and reliably even when an accident occurs, and which avoids the possibility of damaging the surface of the disk, such a clamp mechanism is shown in, for example, FIGS. 3-5 (refer to Japanese Patent Laid-open No. 46652/1988).
Referring to FIG. 3, a reference numeral 101 denotes a clamp body, which has at the upper portion thereof a reference surface 101a used to place thereon a disk 102 which is used as a storage medium, such as a magnetic disk or an optical disk, and which is adapted to be rotated unitarily with a rotary shaft 103 by a motor (not shown) and rotate the disk 102. The clamp body 101 is provided therein with three slidable shafts 104, the lower end portions of which are fitted in the recesses in and held firmly by a guide plate 105 positioned in the bottom portion of the clamp body 101. The slidable shafts 104 are provided at their upper ends with claws 106, by which the disk 102 is securely pressed and clamped.
As shown in FIG. 5, each slidable shaft 104 is provided in its circumferential surface with a lead groove 107 inclined at a predetermined angle, and a guide pin 108 engaged with this lead groove 107 is fixed horizontally to the inner surface of the side wall of the clamp body 101. Therefore, owing to the engagement of the lead groove 107 and locking pin 108 with each other, the slidable shaft 104 is turned around the axis thereof as it is vertically moved.
The driving shaft 109 is moved vertically by an operation of a driving unit (not shown) so as to lift or lower the slidable shafts 104 via the guide plate 105, whereby the slidable shafts 104 are moved slidingly in the vertical direction as they are turned horizontally by a cam mechanism consisting of the lead grooves 107 and locking pins 108. During this time, the claws 106 are turned radially outward as shown in FIG. 4, to stably clamp the disk 102 owing to the pressures of compression springs 110 imparted to the claws 106. When the disk 102 is thus clamped, it is turned by rotating the rotary shaft 103 by the motor, and the information written on the disk 102 is read by a magnetic head 112 provided on a carriage 111.
During an operation of taking out this disk 102 from the reference surface 101a, the driving shaft 109 moves up, and the slidable shafts 104 turn around their axes owing to the cam mechanism consisting of the lead grooves 107 and guide pins 108 with the claws turning inward toward one another up to a position shown by two-dot chain line in FIG. 4.
When the slidable shafts 104 are pressed down in such a conventional clamp mechanism for disks, they are moved slidingly in the downward direction as they are turned by the cam mechanisms consisting of the lead grooves 107 and locking pins 108. During this time, the claws 106 are turned radially outward farther away from one another from the position shown by two-dot chain line in FIG. 4, to clamp the circumferential portion of a central hole 102a in the disk 102. Accordingly, it is necessary that the clamp body 101 be provided in its upper end surface with spaces for allowing the claws 106 to be turned therein. Due to these spaces, the dimensions of the claws 106 cannot be increased, and the number of the claws 106 which can be housed in the upper end surface of the clamp body 101 is three at most, i.e., this number cannot be increased, either. The surface area of the parts of the circumferential portion of the central hole 102a in the disk 102 which are thus clamped by the small-sized small number of clamps 106 is around 10% of a total surface area of the same circumferential portion.
A magnetic disk subjected to a magnetic disk inspection apparatus is rotated at a high speed of 3600 r.p.m. In order to reduce the starting time, during which the number of revolutions per minute of the magnetic disk is increased to this level, and the stopping time, during which the number of revolutions per minute thereof is decreased from this level to zero, it is necessary that the magnetic disk be clamped with a large pressing force so as to prevent the magnetic disk from slipping. When the magnetic disk is then clamped with a large pressing force by the claws 106, the clamping surface of which is as small as about 10% of a total surface area of the circumferential portion of the central hole in the magnetic disk as in this conventional example, the magnetic disk would be bent if the surface accuracy of the reference surface 101a of the clamp body 101 is low, and the degree of such bend of the magnetic disk would further increase due to the flexure of the magnetic disk itself. Therefore, when such a bent magnetic disk is measured with a magnetic disk inspection apparatus, the information which is originally written on the magnetic disk, and which is not defective, is detected as an error, i.e., the information written on the disk cannot be read accurately and speedily by a transducer consisting of a magnetic head or an optical head.